Metal ingots, billets and other castparts may be formed by a casting process which utilizes a vertically oriented mold situated above a large casting pit beneath the floor level of the metal casting facility, although this invention may also be utilized in horizontal molds. The lower component of the vertical casting mold is a starting block. When the casting process begins, the starting blocks are in their upward-most position and in the molds. As molten metal is poured into the mold bore or cavity and cooled (typically by water), the starting block is slowly lowered at a pre-determined rate by a hydraulic cylinder or other device. As the starting block is lowered, solidified metal or aluminum emerges from the bottom of the mold and ingots, rounds or billets of various geometries are formed, which may also be referred to herein as castparts.
While the invention applies to the casting of metals in general, including without limitation, aluminum, brass, lead, zinc, magnesium, copper, steel, etc., the examples given and preferred embodiment disclosed may be directed to aluminum, and therefore the term aluminum or molten metal may be used throughout for consistency even though the invention applies more generally to metals.
While there are numerous ways to achieve and configure a vertical casting arrangement, FIG. 1 illustrates one example. In FIG. 1, the vertical casting of aluminum generally occurs beneath the elevation level of the factory floor in a casting pit. Directly beneath the casting pit floor 101a is a caisson 103, in which the hydraulic cylinder barrel 102 for the hydraulic cylinder is placed.
As shown in FIG. 1, the components of the lower portion of a typical vertical aluminum casting apparatus, shown within a casting pit 101 and a caisson 103, are a hydraulic cylinder barrel 102, a ram 106, a mounting base housing 105, a platen 107 and a bottom block 108 (also referred to as a starting head or starting block base), all shown at elevations below the casting facility floor 104.
The mounting base housing 105 is mounted to the floor 101a of the casting pit 101, below which is the caisson 103. The caisson 103 is defined by its side walls 103b and its floor 103a. 
A typical mold table assembly 110 is also shown in FIG. 1, which can be tilted as shown by hydraulic cylinder 111 pushing mold table tilt arm 110a such that it pivots about point 112 and thereby raises and rotates the main casting frame assembly, as shown in FIG. 1. There are also mold table carriages which allow the mold table assemblies to be moved to and from the casting position above the casting pit.
FIG. 1 further shows the platen 107 and starting block base 108 partially descended into the casting pit 101 with castpart 113 (which may be an ingot or a billet) being partially formed. Castpart 113 is on the starting block base 108, which may include a starting head or bottom block, which usually (but not always) sits on the starting block base 108, all of which is known in the art and need not therefore be shown or described in greater detail. While the term starting block is used for item 108, it should be noted that the terms bottom block and starting head are also used in the industry to refer to item 108, bottom block is typically used when an ingot is being cast and starting head, when a billet is being cast.
While the starting block base 108 in FIG. 1 only shows one starting block 108 and pedestal, there are typically several of each mounted on each starting block base, which simultaneously cast billets, special tapers or configurations, or ingots as the starting block is lowered during the casting process.
When hydraulic fluid is introduced into the hydraulic cylinder at sufficient pressure, the ram 106, and consequently the starting block 108, are raised to the desired elevation start level for the casting process, which is when the starting blocks are within the mold table assembly 110.
The lowering of the starting block 108 is accomplished by metering the hydraulic fluid from the cylinder at a pre-determined rate, thereby lowering the ram 106 and consequently the starting block at a pre-determined and controlled rate. The mold is controllably cooled during the process to assist in the solidification of the emerging ingots or billets, typically using water cooling means. Although the use of a hydraulic cylinder is referred to herein, it will be appreciated by those of ordinary skill in the art that there are other mechanisms and ways which may be utilized to lower the platen.
There are numerous mold and casting technologies that fit into mold tables, and no one in particular is required to practice the various embodiments of this invention, since they are known by those of ordinary skill in the art.
The upper side of the typical mold table operatively connects to, or interacts with, the metal distribution system. The typical mold table also operatively connects to the molds which it houses.
When metal is cast using a continuous cast vertical mold, the molten metal is cooled in the mold and continuously emerges from the lower end of the mold as the starting block base is lowered. The emerging billet, ingot or other configuration is intended to be sufficiently solidified such that it maintains its desired profile, taper or other desired configuration. In some casting technologies, there may be an air gap between the emerging solidified metal and the permeable ring wall, while in others there may be direct contact. Below that, there is also a mold air cavity between the emerging solidified metal and the lower portion of the mold and related equipment.
Once casting is complete, the castparts, billets in this example, are removed from the bottom block.
The casting process is initiated by the introduction of molten metal into the mold cavity and the solidification of the molten metal through the mold cavity occurs by the application of a cooling fluid such as water. The cooling fluid is applied around the perimeter of the mold cavity and in the process, causes the walls of the mold cavity to cool. As the mold cavity wall is cooled the molten metal adjacent the wall generally solidifies and shrinkage occurs around the solidifying surface of the castpart. The shrinkage of the castpart then causes the solidifying castpart to shrink back away from the cooler mold wall, resulting in some re-melting of solidifying surface of the castpart and expansion back to the mold wall. This solidification process occurs and the resulting castpart emerges out of the mold cavity with a solidified outer surface or skin and the inner core of the castpart is still in its molten state. A continuous supply of cooling fluid is applied to the perimeter of the solidifying castpart emerging from the mold cavity.
The volume of cooling fluid supplied to the emerging castpart can be significant and if left uncontrolled, it will run down the side of the outer surface of the castpart and cause further cooling and solidification of the core of the castpart. The exposure of the outer surface of the castpart to the dripping or flowing cooling fluid after the initial direct chill of the emerging castpart alters the cooling characteristics of the castpart and the metallurgical characteristics of the resulting castpart. The process of continuous casting in general results in a relatively fast solidification of the exterior of the castpart (especially for larger castparts such as ingots) but the interior still remains in some status between molten and solidified. This results in internal stresses being imposed between the various internal locations in the castpart and may result in undesirable imperfections and defects.
It is desirable to control the flow and cooling effect of the cooling fluid after its initial direct chill of the castpart. The direct chill of the cooling fluid solidifying the outer surface or skin of the castpart causes internal stresses in the metallic structure; however if the temperature of the core of the solidifying castpart is allowed to remain high for a period after the initial direct chilling, an annealing occurs within the castpart relieving shrinkage stress. This is especially true of some of the more desired alloyed materials such as those used in the aerospace industry, such as series 2XXX and/or 7XXX alloys.
If the excess cooling fluid is not sufficiently controlled and runs down the side of the cooling castpart, it causes unwanted additional cooling of the core of the castpart and impedes the desired annealing process in the castpart.
Wiper type systems have been long used in the industry to control the flow of excess cooling fluid on the surface of the cooling castpart. These prior wiper systems were developed to control and/or divert the coolant away from the lower portions of the solidifying castpart. A wiper generally conforms to the outer surface of the castpart and is in contact around that outer surface. A wiper is similar in some ways to a squeegee used on a window and is mounted relative to the castpart such that the coolant is diverted away from and off the surface of the castpart.
It has been common in the industry to use wipers made of silicone, inflatable rubber-type wipers, or what is commonly referred to as air knives, to accomplish the wiping or diversion of the undesired excess cooling fluid. A wiper is generally configured annularly around the particular castpart and is designed to be in contact with the outer surface of the castpart. The wiper generally diverts the cooling fluid away from the outer surface of the castpart so that it descends into the casting pit away from the surface of the castpart to avoid an undesirable cooling effect.
The traditional use of a wiper system has been to have a fixed or static location of the wiper far enough below the mold to prevent overheating in a steady state or second transitory stage, and close enough to the mold so that the castpart could retain sufficient heat to cause an annealing effect on the castpart. At or near the start up of these traditional systems, the solidifying castpart would pass through the wipers but there is a time when extra water would become trapped between a wiper, starting block or head and the castpart for a period of time (normally minutes). This additional water at startup results in increased and undesirable cooling of the castpart and may also allow cooling fluid to get into the starting block area and increase the probability of a crack forming at or near the butt portion of the castpart during or after solidification. In some embodiments of this invention, the wiper is moved sufficiently below the casting mold and castpart starting block to avoid mis-directing coolant to the starting block or elsewhere during the startup phase or stage.
It is therefore an object of some embodiments of this invention to provide a new wiper actuator and a new process to better position the coolant control system, or wiper, relative to the cast length. This object is to optimize the timing and positions of the coolant or wiper control system relative to the mold to result in a better annealing of the castpart while minimizing capture or trapping of undesirable coolant in the starting block or starting head.
The bottom or base of the solidified castpart may be referred to as the butt and the butt of the castpart is an area where a high incidence of cracks and other undesirable potential castpart defects occur. If cracks develop in the butt portion of the castpart, the castpart is generally scrapped, the molten metal must be remelted and purified all over again. It is costly to have to scrap an entire casting due to a crack in the butt portion of the ingot or castpart.
This invention provides a cooling fluid or wiper control system which more effectively uses, places and moves the wiper during stages of the casting process to provide a better controlled cooling of the solidified castpart. The prior art placement of a wiper in one position relative to the castpart during the entire cast does not as effectively optimize the cooling of the castpart as compared to this invention. It is important that the castpart cooling be controlled and optimized during startup, the transient heat-up stage and then during steady state.
It is therefore an objective of some embodiments of this invention to provide a cooling fluid and wiper control system which more effectively controls the wiper position and movement during all three stages of casting, namely during startup, the transient heat-up stage and the second transitory stage.
In some embodiments of this invention this objective may be met by starting the wiper away from the solidifying metal and cooling fluid during startup, rapidly moving the wiper to the solidifying castpart during the transient heat-up stage, and then controlling the movement and location of the wiper in a direction away from the mold during the second transitory stage of casting.
Other objects, features, and advantages of this invention will appear from the specification, claims, and accompanying drawings which form a part hereof. In carrying out the objects of this invention, it is to be understood that its essential features are susceptible to change in design and structural arrangement, with only one practical and preferred embodiment being illustrated in the accompanying drawings, as required.